Miniature inductor

ABSTRACT

Inductors which can be constructed in a simple and compact manner and with closely controllable and uniform characteristics, including a stack of plates of ferromagnetic material, each plate having a flat spiral coil deposited thereon. Alternate plates are formed with central holes, and an electrical conductor extends through each hole to interconnect the inner turns of a pair of coils with a minimum disturbance of the magnetic fields established by the coils. Each pair of coils which are interconnected at their inner turns spiral in opposite directions so that a current passing serially through the coils creates additive magnetic fields.

United States Patent [191 Felkner [4 1 Nov. 12, 1974 MINIATURE INDUCTOR [75] Inventor: Darrel Felkner, Playa Del Rey,

Calif.

[73] Assignee: Vangaurd Electronics Company,

Inc., Inglewood, Calif.

22 Filed: Dec. 11, 1972 211 Appl. No.2 313,647

[52] US. Cl. 336/200, 336/232 [51] Int. Cl. H0lt 27/30 [58] Field of Search 336/200, 232, 221

[56] References Cited UNITED STATES PATENTS 2,014,524 9/1935 Franz 336/200 2,629,860 2/1953 Chesus et a1 336/200 X 2,786,187 3/1957 Nims 336/200 X 2,911,605 11/1959 Wales, Jr. 336/200 3,185,947 5/1965 Freymodsson 336/232 X 3,483,499 12/1969 Lugten 336/200 X 3,504,276 3/1970 Proctor et a1 336/200 FOREIGN PATENTS OR APPLICATIONS 993,265 5/1965 Great Britain 336/200 Primary ExaminerThomas J. Kozma Attorney, Agent, or FirmLindenberg, Freilich, Wasserman, Rosen & Fernandez [57] ABSTRACT Inductors which can be constructed in a simple and compact manner and with closely controllable and uniform characteristics, including a stack of plates of ferromagnetic material, each plate having a Hat spiral coil deposited thereon. Alternate plates are formed with central holes, and an electrical conductor extends through each hole to interconnect the inner turns of a pair of coils with a minimum disturbance of the magnetic fields established by the coils. Each pair of coils which are interconnected at their inner turns spiral in opposite directions so that a current passing serially through the .coils creates additive magnetic fields.

3 Claims, 3 Drawing Figures MINIATURE INDUCTOR BACKGROUND OF THE INVENTION This invention relates to inductors.

One type of inductor suitable for use in integrated circuits and other miniature applications includes a stack of ferromagnetic plates and flat spiral coils deposited on the plates. The interconnection of the stack of coils is difficult to achieve in a manner that does not increase the size of the inductor or affect its operating characteristics. The innermost turn of each coil can be connected to the outermost turn of the next coil of the stack by a thin wire that extends radially across the coil. However, such a wire tends to increase the spacing of the plates at one side, which increases the size of the stack and necessitates mounting devices to prevent breakage due to localized pressure. In addition, current passing through the radially extending wires produce magnetic fields of a different orientation than the main field produced by the spiralling coils, so that-the shape of the magnetic field is difficult to accurately predict and therefore the characteristics of the inductor are difficult to predict.

SUMMARY OF THE INVENTION In accordance with one embodiment of the present invention, an inductor is provided which is compact, rugged, and of closely and uniformly controllable characteristics. The inductor includes a stack of plates of ferromagnetic material, and fiat spiral coils deposited on the plates. Alternate plates of the stack have central holes, and the inner turns of each pair of coils are interconnected by a conductor that passes through one of the holes. The outer turns of the coils are interconnected by conductors that extend around the edges of the plates.

The interconnection of the coils through holes in the plates eliminates the need for wires or the like to extend radially across the coils to interconnect them. The connectors of the invention therefore eliminate the disruptive magnetic fields that would be created by radially extending wires as well as eliminating the need for additional spacing and mounting to accommodate such radial wires. The use of deposited or etched coils permits very close control of the coil shapes, and this close control combined with the elimination of disruptive magnetic fields results in inductors of high uniformity and closely controllable characteristics.

Each central conductor that connects the inner turns ofa pair of coils, is formed by a thin layer of conductive material lying on the wall of the hole in the ferromagnetic plate and on the face thereof which supports a coil. Such a layer can be formed at the same time as the coil is formed on the plate. A pair of plates is assembled by laying the plate with the hole therein on top of the coil of another plate. The central conductor will then lie adjacent to the coil on the bottommost plate, and can be connected thereto by a simple solder or weld joint. Similarly, the outer conductors which interconnect the outer turns of pairs of coils can be formed by thin layers of conductive material that extend from the outermost turns of the coils to the edges of the plates and along border regions of the plates. A pair of such outer conductors can be connected together by a solder or weld joint.

The novel features of the invention are set forth with particularity in the appended claims. The invention will best be understood from the following description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an inductor constructed in accordance with the present invention shown mounted on a circuit board;

FIG. 2 is a partial exploded perspective view of the inductor of FIG. 1; and

FIG. 3 is a sectional view taken on the line 33 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates an inductor 10 which includes six plates or layers 11-16 of ferromagnetic material arranged in a stack, and six coils 11C-16C of a flat spiral shape disposed on the plates. The inductor 10 is mounted on a circuit board 18 that includes a pair of conductive strips 20, 22. One of the strips 20 is connected to a terminal 24 on the bottommost plate 16, while the other strip 22 is connected to a terminal 26 on the topmost plate 11. The coils 11C-16C are interconnected so that a current passing through the conductive strips 20, 22 of the circuit board passes serially through all of the coils.

As also illustrated in FIGS. 2 and 3, the inductor 10 is constructed of three substantially identical subassemblies 31, 32, and 33, each subassembly including two ferromagnetic plates and the two coils thereon. FIG. 2 illustrates one of these subassemblies 31 which includes the two plates 11 and 12 and their coils 11C and 12C. The two coils 11C and 12C are formed in spiral patterns on their respective ferromagnetic plates, but the coils spiral in opposite directions. That is, the coil 11C spirals outwardly in a clockwise direction as viewed from the upper surface 42 on which the coil is deposited, while the other coil 12C spirals outwardly in a counterclockwise direction as viewed from the upper surface 44 of its plate. The two ferromagnetic plates l1, 12 are similar, except that one of them 11 has a central hole 46 extending through the plate from its upper surface 42 to its lower surface 48, while the other plate 12 does not have such a hole. I

In order to facilitate connections to the coils 1 1C and 12C, additional conductive regions are formed on the plates. An inner conductive region 11D which is formed on the plate 11, extends from the inner turn of the coil 11C to the edge of the hole 46, and extends along the wall of the hole to a location near the lower face 48 of the plate. An outer connective region 11E which is formed on the plate extends from the outermost turn of the coil to the outer edge of the plate and along the perimeter 50 of the plate towards the lower face 48. Similarly, the lower plate includes a central conductive region 12D at the innermost turn of the coil 12C, and an outer conductive region 12E extending from the outermost turn and along the perimeter 52 of the plate 12 towards the lower face 54 of the plate.

The subassembly 31 is assembled by laying the plates together with the lower face 48 of the plate 1 l disposed facewise adjacent to the upper face 44 of a plate 12, with the coil 12C between them. The innermost turns of the two coils 1 1C and 12C are electrically connected The other subassemblies 32 and 33 are similarly constructed, with the innermost turns of the coils 13C and 14C connected by' a weld 58 and the innermost turns of the coils 15C and 16C connected by a weld 60. The three subassemblies 31, 32 and 33 are then stacked on one another as illustrated in FIG. 3. The outermost turns of certain coils are then connected together so that all of the coils are electrically connected in series. This is accomplished by forming a weld 62 to connect the outer conductive region 12E and 13E on the plates 12 and 13. Similarly, a weld 64 connects the outer conductive regions 14E and 15E on the two plates 14 and 15. Connections to the conductive strips 20, 22 of the circuit board are accomplished by welding the opposite ends of a wire 66 to the outer conductive region 11E and to the strip 22, and by forming a weld 68 that connects the outer conductive region 16E to the conductive strip 20. It may be noted that the middle subassembly 32 is rotated 180 from the other subassemblies 31, 33 so that the outer conductive regions 13E and 14B will lie adjacent to corresponding outer conductive rependicular to the axis 70 so there is a minimal disrup- 3 tion of the desired magnetic field. Thecurrent does pass in an axial direction between the successive coils, but these axial paths are short, and therefore cause a minimum of disruption of the principal magnetic field.

Each of the plate-coil assemblies is constructed by forming a layer of conductive material such as copper on a plate or substrate of ferromagnetic material, that is, on a substrate of material of high permeability. The ferromagnetic substrate is preferably of a material which has'a high resistivity, such as a ferrite. This permits the coil to be formed directly on the ferromagnetic material without the need for an insulative layer between them. The forming can be performed in a variety of ways, as by vapor deposition through a mask, electroplating at activated regions, or by etching away an adhesively mounted layer of conductive material. All of these methods, which involve the forming of a uniformly thin layer of a selected shape on a substrate, provide close control of the shape of the conductive material, so that high uniformity can be obtained. The

uniformity and ruggedness of the inductor is relatively high, as compared to inductors of a similar type which utilize wires extending from the center turn of each coil to the outer turn of the next succeeding coil to interconnect the coils. In the inductor 10 of the present invention, no such radially extending wires are required, so that each ferromagnetic plate can be mounted directly on the flat coil of another plate. This provides a large support area for each plate and enables the inductor to be made very compact.

The inductor l0 may be made of a small size to facilitate its use with miniature circuits. Thus, for example, each ferromagnetic plate may have a width and length which are each 0.2 inch and a thickness of 0.02 inch, while each coil may have a thickness of 0.005 inch and a width along the spiral strip of 0.01 inch. The inductor may be made highly rugged by encapsulating it in plastic or the like.

Thus, the invention provides an inductor of closely controllable characteristics and which is rugged and compact. The inductor includes several subassemblies, each assembly having a pair of ferromagnetic substrates and a pair of substantially flat spiral coils, the coils spiralling in opposite directions (when both are viewed from the same direction) and the centers of the coils being connected together. The coils may be held spaced from each other by one of the ferromagnetic plates and may be interconnected by connecting means that extends through one of the plates to connect the innermost turns of the coils. The subassemblies are stacked on one another and the outer turns are connected together so that current passes serially through all of the coils in directions that result in the magnetic fields of the coils adding.

Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art and consequently it is intended that the claims be interpreted to cover such modifications and equivalents.

What is claimed is:

1. An inductor comprising:

a plurality of plates of ferromagnetic material arranged in a stack, alternate plates of said stack hav-' ing central holes extending completely therethrough; and

a plurality of coils disposed on said plates, each coil forming a spiral extending in substantially a plane on a face of a plate, and the coils on pairs of adjacent plates being wound in opposite directions of spiralling, the coils on the plates that have central holes extending over the edges of the holes and along the walls of the holes and the coil portions lying on the hole walls being integral with the coil portions that extend in a spiral on the face of the plate;

a plurality of first connector means, each including a quantity of conductive material joined to a coil portion that lies on the wall of a plate hole and joined to the center portion of a coil on an adjacent plate; and

a plurality of second connector means, each interconnecting the outer portions of the coils which lie on two plates whose coil center portions are unconnected to each other.

2. The inductor described in-claim 1 wherein:

the central hole in each of said alternate plates has a diameter more than twice the thickness of the plate, whereby to facilitate the projection of a soldering tool or the like into the hole to form the quantity of conductive material that joins the coils.

3. The inductor described in claim 1 wherein: said first connector means is a single quantity of conductive material solidified onto the coil portions. 

1. An inductor comprising: a plurality of plates of ferromagnetic material arranged in a stack, alternate plates of said stack having central holes extending completely therethrough; and a plurality of coils disposed on said plates, each coil forming a spiral extending in substantially a plane on a face of a plate, and the coils on pairs of adjacent plates being wound in opposite directions of spiralling, the coils on the plates that have central holes extending over the edges of the holes and along the walls of the holes and the coil portions lying on the hole walls being integral with the coil portions that extend in a spiral on the face of the plate; a plurality of first connector means, each including a quantity of conductive material joined to a coil portion that lies on the wall of a plate hole and joined to the center portion of a coil on an adjacent plate; and a plurality of second connector means, each interconnecting the outer portions of the coils which lie on two plates whose coil center portions are unconnected to each other.
 2. The inductor described in claim 1 wherein: the central hole in each of said alternate plates has a diameter more than twice the thickness of the plate, whereby to facilitate the projection of a soldering tool or the like into the hole to form the quantity of conductive material that joins the coils.
 3. The inductor described in claim 1 wherein: said first connector means is a single quantity of conductive material solidified onto the coil portions. 